The applicant has produced a brake lever of the above kind in large amounts for many years. This brake lever containing a slack adjuster for keeping the slack or distance between the brake linings and the brake drum constant irrespective of the brake lining wear is very well known in the art.
The brake lever has the general function of transmitting the brake force from a brake cylinder to a splined S-cam shaft, on which it is mounted. The main parts of the slack adjuster in the brake lever are a worm wheel mounted on the S-cam shaft and a worm screw meshing with the worm wheel. A slack adjusting movement may be transmitted from a control unit to the worm screw via the following parts coaxially arranged on the worm screw: a locking sleeve and a clutch sleeve, which are connected by means of a one-way clutch in the form of a locking spring, the clutch sleeve being connected to the worm screw by the toothed conical clutch referred to under the heading "Technical Field". This clutch is held engaged by a powerful clutch spring acting axially on the worm screw.
The primary function of the toothed conical clutch is to disconnect the adjusting mechanism during the elasticity part of the brake application so as to obtain a true slack adjusting function. During the adjustment, which occurs at brake release, the clutch is engaged and transmits an angular movement and a torque, the latter being great enough for affecting slack adjustment.
The clutch, however, has also to allow a manual rotation of the worm screw at replacement of worn out brake linings and at installation of the lever, which means that the maximum torque which may be transmitted shall not be too high.
In the present design with a certain number of symmetrical teeth in the clutch a balance between the above two factors has been reached with a certain angle between each tooth flank and the normal; in a practical case this angle is 68.degree. or in total 136.degree. between the two flanks.
It has appeared that the main reason for performance failure of the slack adjuster is that the conical clutch slips due to worn out teeth.